Method for coating golf balls

Abstract: Disclosed is a method for coating a golf ball, wherein coating efficiency of paint is high and a uniform coating can be formed. According to the method, a paint is sprayed over a golf ball moving with rotation on the circumference of a circle having a diameter of 0.5 to 1.5 m from a disc charged with 60,000 to 130,000 V, which is rotating at 20,000 to 40,000 rpm and is inclined or moving in the vertical direction, or a paint is sprayed in a direction at an angle of 45° or less to the horizontal direction from a disc charged with the above voltage, which is rotating at the above number of revolutions, to coat the golf ball so that a ratio of the maximum film thickness part to the minimum film thickness part may be 1.5 or less after one round coating.

Description: The present invention relates to a method for coating a golf ball with paint. More particularly, it relates to a method for coating a golf ball with paint, wherein coating efficiency of the paint is high and the resulting coating is uniform in thickness. In order to make the appearance of golf balls beautiful and to prevent stains from adhering onto the surface of golf balls, the surface of the golf ball is coated with enamel and clear paint or coated with clear paint alone. As a prior art method of coating golf balls with enamel paint or clear paint by coating once, an air gun coating has hitherto been used. By this method the whole golf ball can be coated with paint by moving the air gun vertically. However, the air gun coating has a problem in that the coated film is non-uniform, which results in appearance deterioration. Further, in a disc type electrostatic coating wherein paint is coated on an article from a front direction, a prior art method is known for coating the enamel paint or clear paint, by coating once. In this electrostatic coating, since the golf ball has no electric conductivity, a conductive agent obtained by diluting a quaternary ammonium salt with alcohol is applied on the surface of the golf ball. After drying, the golf ball is supported (grounded) by placing on three metal needles to impart electroconductivity to the golf ball. After the golf ball is subjected to the above electroconducting treatment, a charged paint is sprayed onto the surface of the golf ball to give a golf ball which has been coated uniformly. However, using this method, a satisfactory coating can be formed on an article having relatively large area, but the coating efficiency is inferior for an article having a relatively small area such as golf ball. Two or more times as much paint is required in comparison with the air gun system. Further, there is also suggested a coating method comprising spraying a charged paint over a golf ball moving on the circumference of a circle from the centre part of an electrostatic coater. However, when using this method, the charged paint is attracted to metal needles supporting the golf ball and, therefore, the lower half of the golf ball is not sufficiently coated. In order to coat the whole golf ball uniformly, the golf ball must be turned over after moving around on the circumference of the circle and moved on the circumference of the circle one more time. Thus, coating efficiency is good but productivity is low. As described above, a conventional method for coating a golf ball has an associated problem in that a coated film is not uniformly formed and the coating efficiency of paint is inferior. Further, the method having good coating efficiency lacks in productivity. EP-A-0 601 861 relates to a method of coating a golf ball with a paint and is comprised in the state of the art by virtue of Article 54(3) EPC. The main object of the present invention is to provide a method for coating a golf ball wherein a uniform coating can be formed and coating efficiency of paint is good and, further, productivity is also good. This object as well as other subjects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawing of which: Fig. 1 is a schematic diagram illustrating the surface part of the golf ball. The present invention provides a method for coating a golf ball, the method comprising spraying a paint over a golf ball moving with rotation on the circumference of a circle having a diameter from of 0.5 to 1.5 m, the paint being sprayed from an inclined disc charged with from 60,000 to 130,000 V and revolving at from 20,000 to 40,000 rpm, whereby the ratio of the maximum film thickness part to the minimum film thickness part is 1.5 or less after one round coating. By the term one round coating (also described hereinafter by a single coating round) is meant to describe movement of the golf ball once around the circumference of the circle. The method according to the present invention enables a golf ball to be coated with a uniform film thickness of paint and with good coating efficiency after one round coating. It is necessary that the diameter of the circle of which the golf ball rotates around the circumference thereof is 0.5 to 1.5 m, preferably 0.7 to 1.1 m. That is, good coating properties (uniform coat-forming properties) and high coating efficiency are accomplished by setting the diameter of the circle within a range of 0.5 to 1.5 m. When the diameter of the circle is smaller than the above range, the paint does not adhere to the golf ball and it becomes difficult to obtain an uniform coating. On the other hand, when the diameter of the circle is larger than the above range, the coating efficiency deteriorates. It is necessary that the disc for spraying the paint rotates at 20,000 to 40,000 rpm, preferably 25,000 to 35,000 rpm. That is, good coating properties can be obtained by rotating the disc at the number of revolutions within the above range. When the number of revolutions of the disc is smaller than the above range, particles of the paint become large, which results in irregular coating. On the other hand, when the number of revolutions of the disc is larger than the above range, particles of the paint become too small and the paint can not reach the golf ball easily, which also results in irregular coating. Further, it is necessary that the charge to be applied on the disc is 60,000 to 130,000 V, preferably 80,000 to 100,000 V. That is, good coating properties can be obtained by setting the charge to be applied on the disc within the above range. When the charge to be applied on the disc is smaller than the above range, coating efficiency deteriorates. On the other hand, when the charge to be applied on the disc is larger than the above range, safety problems arise and power consumption increases, thereby increasing the cost of coating the golf ball. It is preferred that the diameter of the disc is 200 mm or less, particularly 50 to 150 mm. When the diameter of the disc is within the above range, the disc can be easily revolved at the above number of revolutions. Further, by connecting a body of the electrostatic coater with the disc via an air bearing, the disc can be revolved more stably at the above number of revolutions. In order to obtain an uniform coating by one round coating, the disc is inclined, in addition to the above condition. That is, by inclining the disc, the region to be sprayed with the paint widens and it becomes possible to coat the whole golf ball uniformly. It is preferred that the disc is inclined at an angle of 3 to 15° to a horizontal direction. When the angle of the disc to the horizontal direction is smaller than the above range, the region to be sprayed with the paint is not widened. On the other hand, when the angle to the horizontal direction of the disc is larger than the above range, the region to be sprayed with the paint is too wide, which results in deterioration of coating efficiency and generation of irregular coating. As a means to obtain a uniform coating by a single coating round, it is preferred to move the disc vertically in addition to inclining the disc. That is, by moving the disc vertically, the region to be sprayed with the paint widens and it becomes possible to coat the whole golf ball uniformly. Further, the distance at the time of moving the disc, in the vertical direction is, as shown in Examples described hereinafter, within a range between a position which is 30 cm away from the position of the golf ball in the up direction and a position which is 10 cm away from the position of the golf ball in the down direction, the position of the golf ball being 0. As a matter of course, the above two means are used in a combination, that is, the disc is inclined and, at the same time, the disc is moved in the vertical direction, in order to obtain an uniform coating by a single coating round. It is preferred that electroconductivity is imparted to the golf ball in advance by coating it with a solution obtained by diluting a quaternary ammonium salt with alcohols, having a concentration of about 1 to 2% by weight. Further, it is preferred that the golf ball is supported on three metal needles at the time of coating. In order to obtain an uniform coating, it is preferred that the golf ball is rotating at 30 to 100 rpm at the time of coating. When the golf ball is rotating at the above number of revolutions, it becomes possible to coat the golf ball uniformly. Examples of the paint to be used for coating include urethane and epoxy paints, but the paint is not specifically limited, and any paint known in the art may also be used. In the present invention, there can be formed a coating which has good coating efficiency and high uniformity, i.e. a ratio of the maximum film thickness part to the minimum film thickness part is 1.5 or less, by means of charge and number of revolutions of the disc, rotation of the golf ball, inclination or vertical movement of the disc, etc. as described above. The golf ball is normally coated in a film thickness of 7 to 60 µm. The present invention exhibits remarkable technical effects, particularly in the formation of the coating having a thickness within the above range. As described above, according to the present invention, there can be formed a uniform coating having good coating efficiency of paint on the golf ball. That is, coating efficiency is high and may be up to about two times as efficient as that of the conventional air gun coating, and uniformity of the coating is high, i.e. a ratio of the maximum film thickness part to the minimum film thickness part is 1.5 or less. Further, according to the present invention, the coating can be completed only by moving the golf ball once around the whole circumference of the circle and productivity of the golf ball coating method is also high. The following Examples and Comparative Examples further illustrate the present invention in detail but are not to be construed to limit the scope thereof. Examples 1 to 9 and Comparative Examples 1 to 8 A paint was coated on the surface of the golf ball according to the following manner and the resulting coating were evaluated. 1. Golf ball to be coated A two-piece solid golf ball obtained by covering a solid core, which was obtained by subjecting a rubber composition to a vulcanizing molding, with a cover composed of an ionomer resin as a main material, the surface of the golf ball was provided with 432 dimples. 2. Coating system Two systems: electrostatic coating, and air gun coating are used as comparison. That is, the electrostatic coating is conducted in Examples 1 to 9 and Comparative Examples 1 to 7, and the air gun coating is conducted in Comparative Example 8. 3. Electrostatic coating The coater to be used is a disc type electrostatic coater, wherein the normal type disc is provided at a position which is slightly upward from that of the golf ball and the paint is sprayed in the downward and diagonal direction. The conditions set for the golf ball and disc when the golf ball is coated with the paint using the above electrostatic coater will be explained below. It is necessary that these items are set as described in Tables 1 to 5. However, it is difficult to describe these items precisely and completely in Tables 1 to 5 because of the limited space and, therefore, they are represented by abbreviations. Abbreviations are shown in parenthesis after the explanation of the respective items. 3-1 Conditions of the golf ball Diameter of the circle wherein the golf ball is moving on its circumference (diameter of circle) Number of revolutions of the golf ball (number of revolutions) 3-2 Conditions of the disc for spraying paint Number of revolutions of disc (number of revolutions) Angle of disc (angle) Moving position of disc in vertical direction (vertical moving position) Upper limit position when position of golf ball is 0 (Upper) Lower limit position when position of golf ball is 0 (Lower) When the upper limit value and the lower limit value are the same, it indicates that the disc is at the rest state without vertical movement. Voltage to be applied on disc (voltage) Shape of disc (shape) I: Normal type disc Direction for dispersing paint: +50° The angle of the direction for dispersing paint is 0 in the horizontal direction and (+) in the downward direction. J: Hat type disc Direction for dispersing paint: +15° K: Well-field type disc Direction for dispersing paint: -8° 3-3 Other coating conditions Paint: Two-pack urethane paint is used. Pigments such as titanium oxide are not present. Moving speed of golf ball: 5 m/minute The electroconductivity is imparted to the golf in advance before coating by immersing it in a solution obtained by diluting a plastic electroconductive agent NC (trade name) manufactured by Cause Co. with isopropyl alcohol so that the concentration may be 1% by weight and after that, drying it until the isopropyl alcohol voltalizes. The golf ball is coated after placing on three iron needles. The amount of the paint per coating is 120 mg. 4. Air gun coating. Coating is conducted by moving the air gun at a moving speed of 5 m/second within a range of 10 cm (upper direction) and 10 cm (lower direction). In that case, the golf ball is rotated at 200 rpm. The amount of the paint per coating is 120 mg. The respective conditions were set about the above-described items and the paint was coated on the golf ball. The conditions of the golf ball at the time of coating, the conditions of the disc and the coating results are shown in Tables 1 to 5 Further, the results of coating are evaluated by uniformity of the coating and coating efficiency of the paint. The uniformity of the coating is evaluated by a ratio of the maximum film thickness to the minimum film thickness. Table 1 illustrates the results of Examples 1 to 3 and Comparative Examples 1 to 2. In Table 1, the difference in results of coating due to a difference in diameter of the circle (i.e. diameter of circle wherein the golf ball is moving on its circumference) is shown. They are described in the order of increasing diameter of circle, i.e. Comparative Example 1, Example 1, Example 2, Example 3 and Comparative Example 2 in this order. In Table 2, the difference in results of coating due to a difference in number of revolutions of disc at the time of coating is shown. The conditions at the time of coating and results of coating are described in the order of increasing number of revolutions of disc, i.e. Comparative Example 4, Example 4, Example 2, Example 5 and Comparative Example 4 in this order. In Table 3, the difference in results of coating due to the difference in the voltage of the disc at the time of coating is shown. The conditions at the time of coating and the results of coating are described in an order of increasing voltage of disc, i.e. Comparative Example 5, Example 6, Example 2 and Example 7 in this order. In Table 4, the difference in results of coating due to the difference in the angle of the disc at the time of coating is shown. The conditions at the time of coating and results of coating are described in the order of increasing angle of disc, i.e. Comparative Example 6, Example 8, Example 2 and Example 9 in this order. In Table 5, the results of coating of Comparative Example 8 according to the air gun coating are shown. In respective Tables, the arrow (←) of the left direction means that the content is the same as those on the left side. The reason why Example 2 is described in Tables 2, 3 and 4 in addition to Table 1 is as follows. Regarding various conditions defined in the present invention, approximately middle conditions are selected in Example 2 so that it is advantageous to know that a change in the results of coating is caused by a change in various conditions. The maximum thickness, the minimum thickness, the film thickness ratio and the coating efficiency of the coating described in the respective Tables are determined as follows. (1) Regarding thickness of coated film Five dimples of the golf ball are picked up at random. Regarding the respective dimples, the thickness of the coated film is measured at the respective positions (A, B, C and D) shown in Fig. 1. The average value is determined by adding these values and the average value is taken as a film thickness at the dimple. Then, the maximum thickness and minimum thickness at five dimples are determined, and a ratio of the maximum film thickness part to the minimum film thickness part is determined as a film thickness ratio. Now referring to Fig. 1, which is a schematic diagram illustrating the surface part of the golf ball, 1 is a dimple and A, B, C and D indicate the following positions, respectively: A: Centre of dimple, i.e. most deep part B: Edge part of dimple C: Intermediate part between centre and edge part of dimple D: Surface part of circumference of dimple (2) Coating efficiency The coating efficiency (R) is determined from an amount of the paint used (amount of paint) and an amount of the paint adhered on the golf ball (coating weight) according to the following equation: R(%) = [(coating weight)/(amount of paint)] x 100. Comparative Example 1 Example 1 Example 2 Example 3 Comparative Example 2 Golf ball: Diameter of circle (m) 0.4 0.6 1.0 1.4 1.6 Number of revolutions (rpm) 50 ← ← ← ← Disc: Number of revolutions (rpm) 30,000 ← ← ← ← Angle (°) 8 ← ← ← ← Vertical moving position Upper (cm) 6 ← ← ← ← Lower (cm) 6 ← ← ← ← Speed (m/minute) 0 ← ← ← ← Voltage (V) 90,000 ← ← ← ← Shape I ← ← ← ← Results of coating: Coated film Maximum thickness (µm) 20.6 19.1 18.9 19.4 21.1 Minimum thickness (µm) 13.0 14.6 15.3 14.5 12.6 Film thickness ratio 1.58 1.31 1.24 1.34 1.67 Paint adhesion efficiency (%) 38 61 67 58 31 Comparative Example 3 Example 4 Example 2 Example 5 Comparative Example 4 Golf ball: Diameter of circle (m) 1.0 ← ← ← ← Number of revolutions (rpm) 50 ← ← ← ← Disc: Number of revolutions (rpm) 18,000 22,000 30,000 38,000 42,000 Angle (°) 8 ← ← ← ← Vertical moving position Upper (cm) 6 ← ← ← ← Lower (cm) 6 ← ← ← ← Speed (m/minute) 0 ← ← ← ← Voltage (V) 90,000 ← ← ← ← Shape I ← ← ← ← Results of coating: Coated film Maximum thickness (µm) 20.7 19.6 18.9 19.5 21.3 Minimum thickness (µm) 12.9 14.4 15.3 14.1 11.9 Film thickness ratio 1.60 1.36 1.24 1.38 1.79 Paint adhesion efficiency (%) 42 62 67 60 59 Comparative Example 5 Example 6 Example 2 Example 7 Golf ball: Diameter of circle (m) 1.0 ← ← ← Number of revolutions (rpm) 50 ← ← ← Disc: Number of revolutions (rpm) 30,000 ← ← ← Angle (°) 8 ← ← ← Vertical moving position Upper (cm) 6 ← ← ← Lower (cm) 6 ← ← ← Speed (m/minute) 0 ← ← ← Voltage (V) 45,000 70,000 90,000 120,000 Shape I ← ← ← Results of coating: Coated film Maximum thickness (µm) 19.9 19.7 18.9 19.7 Minimum thickness (µm) 11.7 14.7 15.3 13.2 Film thickness ratio 1.71 1.34 1.24 1.49 Paint adhesion efficiency (%) 37 56 67 52 Comparative Example 6 Example 8 Example 2 Example 9 Comparative Example 7 Golf ball: Diameter of circle (m) 1.0 ← ← ← ← Number of revolutions (rpm) 50 ← ← ← ← Disc: Number of revolutions (rpm) 30,000 ← ← ← ← Angle (°) 0 3 8 14 16 Vertical moving position Upper (cm) 6 ← ← ← ← Lower (cm) 6 ← ← ← ← Speed (m/minute) 0 ← ← ← ← Voltage (V) 90,000 ← ← ← ← Shape I ← ← ← ← Results of coating: Coated film Maximum thickness (µm) 20.3 18.9 18.9 19.5 20.6 Minimum thickness (µm) 13.1 13.2 15.3 13.2 12.1 Film thickness ratio 1.55 1.43 1.24 1.48 1.70 Paint adhesion efficiency (%) 61 66 67 60 48 Comparative Example 8 Air gun coating Results of coating: Coated film Maximum thickness (µm) 24.6 Minimum thickness (µm) 10.8 Film thickness ratio 2.28 Paint adhesion efficiency (%) 38 As is apparent from the results shown in Table 1, regarding Examples 1 to 3 wherein the diameter of the circle (the diameter of the circle wherein the golf ball is moving on its circumference) is within a range of 0.5 to 1.5 m, the film thickness ration [(maximum film thickness part)/(minimum film thickness part)] was within a range of 1.5 or less and the uniformity of the coating was high and, at the same time, the coating efficiency was high in comparison with Comparative Examples 1 to 2. To the contrary, regarding Comparative Example 1 wherein the diameter of the circle is 0.4 m and is smaller than the above range, the film thickness ratio was 1.58 and exceeded 1.5 and the coating efficiency was low, such as 38%. Further, regarding Comparative Example 2 wherein the diameter of the circle is 1.6 m and is larger than the above range, the film thickness ratio was large such as 1.67 and the uniformity of the coating was insufficient and, further, the coating efficiency was low, such as 31%. As is apparent from the results shown in Table 2, regarding Example 4, Example 2 and Example 5 wherein the number of revolutions of the disc is within a range of 20,000 to 40,000 rpm, the film thickness ratio was 1.5 or less and the uniformity of the coating was high and, further, the coating efficiency exceeded 60% and was high. To the contrary, regarding Comparative Example 3 wherein the number of revolutions of the disc is 18,000 rpm and is smaller than the above range, the film thickness ratio was 1.6 and exceeded 1.5. Further, regarding Comparative Example 4 wherein the number of revolutions of the disc is 42,000 rpm and is larger than the above range, the film thickness ratio was 1.79 and exceeded 1.5 and, further, the uniformity of the coating was insufficient. As is apparent from the results shown in Table 3, regarding Example 6, Example 2 and Example 7 wherein the voltage of the disc is within a range of 60,000 to 130,000 V, the film thickness ratio was 1.5 or less and the uniformity of the coating is high and, further, the coating efficiency was 52% or more and was high. To the contrary, regarding Comparative Example 5 wherein the voltage of the disc is 45,000 V and is smaller than the above range, the film thickness ratio was 1.7 and exceeded 1.5. Further, the uniformity of the coating was insufficient and the coating efficiency was low, such as 37%. As is apparent from the results shown in Table 4, regarding Example 8, Example 2 and Example 9 wherein the angle of the disc is within a range of 3 to 15°, the film thickness ratio was 1.5 or less and the uniformity of the coating was high and, further, the coating efficiency exceeded 60% and was high. To the contrary, regarding Comparative Example 6 wherein the angle of the disc is 0° and is smaller than the above range, the film thickness ratio was 1.55 and exceeded 1.5. Further, regarding Comparative Example 7 wherein the angle of the disc is 16° and is larger than the above range, the film thickness ratio was 1.70 and exceeded 1.5 and, further, the uniformity of the coating was insufficient. As is apparent from the results shown in Table 5, regarding Comparative Example 8, wherein the air gun coating was conducted, the film thickness ratio was 2.26 and exceeded 1.5 and the uniformity of the coating was insufficient.

Claims: A method for coating a golf ball, characterised in that the method comprises spraying a paint over a golf ball moving with rotation on the circumference of a circle having a diameter of from 0.5 to 1.5 m, the paint being sprayed from an inclined disc charged with from 60,000 to 130,000 V and revolving at from 20,000 to 40,000 rpm, whereby the ratio of the maximum film thickness part to the minimum film thickness part is 1.5 or less after one round coating. A method as claimed in claim 1, wherein the inclined disc also moves in a vertical direction. A method as claimed in claim 1 or claim 2, wherein the disc for spraying the paint revolves at from 25,000 to 35,000 rpm. A method as claimed in any one of claims 1 to 3, wherein the disc is charged with from 80,000 to 100,000 V. A method as claimed in any one of claims 1 to 4, wherein the diameter of the disc is 200 mm or less. A method as claimed in claim 5, wherein the diameter of the disc is from 50 to 150 mm. A method as claimed in any one of claims 1 to 6, wherein the golf ball rotates at from 30 to 100 rpm. A method as claimed in any one of claims 1 to 7, wherein the disc is inclined at an angle of from 3 to 15° to the horizontal . A method as claimed in any one of claims 1 to 8, wherein the circle has a diameter of from 0.7 to 1.1 m. A method as claimed in any one of claims 1 to 9, wherein the golf ball is coated with the paint to a film thickness of from 7 to 60 µm.

Inventors: HORIUCHI KUNIYASU, MARUOKA KIYOTO, TAKAHASHI MASATOSHI, YABUKI YOSHIKAZU, HORIUCHI, KUNIYASU, MARUOKA, KIYOTO, TAKAHASHI, MASATOSHI, YABUKI, YOSHIKAZU
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES, LTD.
Application year: 1994
Main classification: B05D1
IPC codes: A63B45, A63B37, B05D7, B05B5, B05D1